I put a 55 cfm fan in the Centaur. Plenty of air and not much noise. The amp does not get very warm even with the 55 cfm when running around 500w CW. 73, Ken, KA0W -- FAQ on WWW: http://www.contesting.com/FAQ/tentec Submissions: tentec@contesting.com Administrative requests: tentec-REQUEST@contesting.com Problems: owner-tentec@contesting.com